This invention relates generally to magnetic disc drives, and more particularly the invention relates to the mounting of magnetic recording discs on a rotatable hub.
A disc drive for magnetically recording data comprises a plurality of discs mounted in spaced relationship on a rotatable hub. As the discs are rotated on the hub, pickup heads move across the disc surfaces for recording or reading digital data on concentric tracks in magnetic film on the disc surfaces.
To reduce the overall size of disc drives, the spindle motors for rotating the hubs have been positioned within the hub rather than external thereto. This has necessitated the use of ferromagnetic steel as the hub material to provide the magnetic return path and insulation between the spindle motor and the recording discs. Since the discs are glass or aluminum, alignment problems can arise when the disc drive is temperature-cycled. For example, shipping specifications call for temperatures down to -40.degree. C., causing the discs to shrink at different rates and magnitudes than the hub and creating interference between the discs and the hub. The interference can result in a slippage of the discs on the hub and introduce a new center of rotation for the discs. This, in turn, introduces off-track errors in recorded data.
Heretofore, attempts at eliminating disc slippage due to temperature cycling have included reducing the diameter of the hub and the application of strips of Teflon tape in parallel axial alignment and radially spaced on the surface of the hub. The tape is supposed to center the discs adequately yet be compliant as the discs move relative to the hub. However, this method has the disadvantages of difficult and time-consuming assembly as well as reliability concerns if the discs peel the tape at the top of the hub. Further, contamination can become a problem since the discs slide down the entire length of the tape during assembly.